1. Field of the Invention
The present invention relates generally to the preparation of microscope sample slides for biological analysis and, more particularly, to an automated method of preparing smeared, stained hematology slides for microscopic analysis.
2. Description of the Prior Art
The microscopic examination of biological specimens on prepared object slides has long been an important technique in diagnostic and other medical evaluations concerning the health of patients. In this regard, the microscopic examination of smeared samples of blood is a particularly important aid to the physician.
One important example of this is the identifying and counting of the different types of white blood cells (leukocytes) found in a smear of whole blood known as a leukocyte differential count as well as other evaluations, such as red cell morphology and platelet sufficiency which require microscopic optical analysis of the blood.
Typically, when, as is generally the case, several different tests are to be run on a sample of blood, a sample of blood is drawn from a patient through a sterile needle in to a vacutainer containing an anti-coagulant and/or certain preservative or fixative agents. The sample is then transferred to the laboratory where, through a series of steps, it is prepared for the tests. The preparation of a smeared specimen slide as for a leukocyte differential count is generally as follows.
Because unmixed whole blood has a tendency to separate into layers of its constituents in order for any subsequent sample withdrawn from the specimen to be representative of the original, the original must be thoroughly mixed. Thus, the first step is normally manually attaching the vacutainer tube to a mixing device to accomplish a thorough mixing of the sample.
A small amount of the mixed sample is then withdrawn from the vacutainer, and a drop of it is placed on a microscope specimen slide. A smear of the blood is then made manually using another glass slide or other device to "wedge" the drop of blood across the slide. The smeared slide is then stained by manually applying to the smear or dipping the slide into an amount of Wrights or similar stain. This is followed by applying an amount of a buffer solution, allowing the buffer to react with the stain and rinsing the slide with a rinse solution. After the slide has been allowed to dry, it is ready for examination under a microscope.
Several attempts have been made to improve or automate various steps involved in the preparation of such blood smears for microscopic examination.
Thus, several devices have been developed in the prior art to maintain biological samples and tubular containers in a homogenized condition. One such device is disclosed in U.S. Pat. No. 3,747,900 to Dilts dated July 24, 1973. That device comprises a D.C. motor-driven, vertical plate to which clips for holding tubes or vials containing the fluid to be mixed are attached by permanent magnets or adhesive nylon strips. Another such prior art device utilizes an adjustably tiltable, motor-driven rotating disc member having a plurality of vial or test tube holding clips permanently secured thereto as disclosed in U.S. Pat. No. 3,163,404 to Kraft, et al. dated Dec. 29, 1964.
While both of these prior art devices may successfully mix fluids, they suffer from several disadvantages. Generally, the clips can accommodate tubes only of a specified diameter, and after a time the clips lose their resiliency and must be replaced. The necessity of using clips at all increases the amount of handling required which, of course, increases the likelihood of vial or tube breakage. In the case of permanently attached clips, it is quite difficult to add or remove tubes to the disc while the disc is rotating.
Several attempts have been made in the prior art to automate the creation of the smear on the blood slide. One such device is illustrated and described in a patent to Levine, et al., U.S. Pat. No. 3,880,111, issued Apr. 29, 1975, which discloses a blood smear device for automatically wedging or creating a blood smear on a specimen slide.
An example of an attempt to automate the staining of the slide is disclosed in a patent to J. B. McCormick, et al., U.S. Pat. No. 3,667,896, issued June 6, 1972.
While these prior art devices represent progress in selected areas, they all suffer certain drawbacks which detract from repeatable consistency in the preparation of stained slides for hematology. Today with the advent of automated and semi-automated devices for examining such slides, consistency in slide preparation, including such areas as the thickness and size of the smear and the coloring and highlighting of the individual blood constituents achieved by staining, is becoming critically important to the achievement of accurate, repeatable results.